Earth’s climate is a complex web of interconnected systems that often behave in unexpected ways. One striking example is how dust from the Sahara Desert in North Africa travels thousands of miles to nourish ecosystems in the Amazon rainforest and deep ocean layers. Similarly, pollution-eating microbes can traverse the atmosphere on winds or fog.
A crucial component of this global network is the Atlantic Meridional Overturning Circulation (AMOC), a vast Atlantic Ocean current system that acts like a planetary conveyor belt. It transports warm water from the tropics northward to Europe and returns cooler water south along the ocean floor.
Human-induced climate change, however, is causing this essential system to slow down, raising concerns about a possible collapse in the near future.
Due to the seriousness of the issue, scientists are actively debating the likelihood and timing of such an event. The most recent research, published in Nature Communications, aims to clarify our understanding of the AMOC and its possible consequences.
Researchers analyzed decades of atmospheric data collected by NASA and used climate simulations to predict changes in the AMOC, which could result in significant shifts for communities worldwide.
“It is well known that the AMOC is a big player in the world’s climate system, and that it is slowing down,” says Mohima Mimi, a climate dynamics researcher at the University of California, Riverside, who led the study.
“What we didn’t know is exactly how the AMOC might impact atmospheric moisture and storms outside the Atlantic region.”
The team discovered that a disrupted AMOC could have significant global climate impacts, as Mimi explains:
“It turns out a weakening AMOC will strengthen storms across parts of North America by the end of the century, particularly along the California coast, while reducing them over Greenland and the Arctic.”
This is because changes in ocean currents influence similar atmospheric systems known as atmospheric rivers.
Atmospheric rivers (ARs) are long, narrow bands of concentrated water vapor in the atmosphere. The most intense ARs can carry up to 15 times the water flowing through the mouth of the Mississippi River.
These atmospheric phenomena have a marked effect on regional climates.
“In California, atmospheric rivers are a double-edged sword,” Mimi says. They deliver up to 50 percent of the yearly rainfall in the western U.S., particularly in California, and are critical to the state’s unstable water supply.
However, they also pose flood risks, frequently causing floods during droughts that threaten lives, damage infrastructure, and affect statewide water quality.
Expanding our view to the planet’s colder regions, atmospheric rivers contribute to warming and ice loss at the poles, with significant implications.
“Over Antarctica, ARs account for 40 to 80 percent of summer meltwater in West Antarctic ice shelves, which threatens ice stability and accelerates global sea level rise,” the researchers explain in their paper.
Additionally, the global frequency of atmospheric rivers could rise by about 50 percent, according to the study.
Atmospheric rivers may also carry more moisture and last longer, reaching higher latitudes as the westerly jet stream shifts poleward due to human-induced warming.
As the AMOC decelerates, it will modify ocean temperatures and reduce atmospheric moisture in the Northern Hemisphere while increasing it in the Southern Hemisphere.
As a result, atmospheric rivers are predicted to become more frequent, bringing increased rainfall to areas such as the east coast of South America, southern Asia, western Europe, parts of the Pacific, and around Antarctica.
The most significant increases are anticipated along the west coast of North America, from Baja California to Alaska.
Conversely, atmospheric rivers might become less common in the Arctic, Greenland, and northern Asia, as cooler air temperatures and lower moisture content accompany a weakened AMOC.
Other regions at lower latitudes, such as northern Australia and the South Pacific, may also see a decline in atmospheric river frequency.
While these scenarios are not set in stone, they depend on industrial activities that are currently increasing greenhouse gas emissions, warming the planet.
On the brighter side, the sometimes-destructive atmospheric rivers also offer opportunities. Research suggests that regions like California could capture more water by restoring natural landscapes, helping to mitigate persistent droughts caused by hotter, drier weather.
Related: Scientists Rule Out a Worst-Case Climate Scenario, But We’re Not Off The Hook
Ultimately, this research underscores the interconnectedness of our planet’s processes. A shift in a single major ocean current can ripple across vast distances, affecting weather systems, enhancing rainfall in the Amazon, and shifting tropical rain belts.
“This research shows that the effects of the AMOC extend far beyond the Atlantic Ocean,” Mimi says.
“Understanding these connections will help us better prepare for future changes in water resources and extreme weather.”
This research was published in Nature Communications.
This article was fact-checked by Michael Irving and edited by Clare Watson. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.
